1. Field of the Invention
The present invention relates to an accident sound detection circuit for efficiently detecting only an accident sound including an accident sound caused by clash of cars and the like and a heavy-braking sound leading to an accident from traffic sounds in an intersection and the like.
2. Description of Related Art
Generally speaking, many traffic accidents happen at an intersection, and hence recording apparatus of traffic accident conditions that record conditions of happened accidents have been proposed. FIG. 21 is a block diagram of, for example, a conventional recording apparatus of traffic accident conditions that is disclosed in Japanese Patent Laid-Open No. 4-338900. In the Figure, numerals 1 and 4 show traffic signals that are allocated at an intersection and have respective signal lamps 1B, 1Y, 1R, 4B, 4Y, and 4R. In addition, 3 is a signal lamp lighting controller sending lighting control signals to respective signal lamps 1B, 1Y, 1R, 4B, 4Y, and 4R via signal lines 2B, 2Y, and 2R, and 5 is a signal lamp symbol generating block that fetches signal lighting condition signals from the signal lamp lighting controller unit 3 and outputs a signal of a color symbol showing a lighting color. Moreover, 6 is a time character generating block generating characters displaying time information (for example, 00:00:00 (o'clock:minutes:seconds)) by coinciding with real time.
Numeral 8 shows an image pickup unit that is used for taking a picture of the vicinity of the intersection and outputs a picture signal. Furthermore, 7 is an adding block that adds signals outputted from the signal lamp symbol generating block 5, time character generating block 6, and image pickup unit 8 and generates a picture signal of the vicinity of the intersection including time and signal lamp lighting conditions. Numeral 10 is an environmental sound detection unit detecting a traffic sound around the intersection, and 9 is an endless recording unit updating and recording the traffic sounds, detected by the environmental sound detection unit 10, and the picture signals, generated by the adding block 7, every determined time.
Numeral 11 is a clash (accident) sound detection circuit judging from the traffic sound detected by the environmental sound detection unit 10 whether it is a clash sound when a car clashes with something or just before it clashes. Further, 12 is a recording control unit that outputs the picture signal and traffic sound before judgement from the endless recording unit 9 to a magnetic recording control unit 13 when a clash sound is judged and makes them recorded. Furthermore, 13a and 13b are output terminals for outputting contents, recorded in the magnetic recording control unit 13, to a magnetic recording and playback unit not shown.
Next, an outline of operation of a conventional apparatus will be described. A sound signal in the vicinity of an intersection is detected by the environmental sound detection unit 10, and is sent to the clash sound detection circuit 11. The clash sound detection circuit 11 discriminates whether the detected sound signal is a clash sound, and if it does that the sound is a clash sound, a clash sound detection signal is sent to the recording control unit 12. The recording control unit 12 records a picture signal and an environmental sound before the clash sound is discriminated by reading a picture signal and an environmental sound from the endless recording unit 9 according to the clash sound detection signal that is sent and recording them in the magnetic recording control unit 13.
In regard to the judgement of whether a detected traffic sound is an accident (clash) sound, the clash sound detection circuit 11 judges the sound to be a clash sound if the level of the inputted sound signal is equal to or more than a predetermined threshold level when the level of the sound is compared with the threshold level. In addition, as a measure against malfunctions, a directional microphone is used in the environmental sound detection unit 10, and hence the microphone does not catch sound signals from places except the intersection. Furthermore, sound signals are inputted after passing through a band-pass filter excluding frequency bands except clash sounds.